1. Technical Field of the Invention
The present invention relates to an electrical wiring structure, an electro-optical device, and an electronic apparatus, which are particularly appropriate for use in an electro-optical device, such as a liquid crystal display device, for example.
2. Description of the Related Art
Hitherto, an electro-optical device such as a liquid crystal display device, in which an electro-optical material such as liquid crystal is interposed between a pair of opposed substrates, has been well known.
The structure of the liquid crystal display device will be more specifically described below. The liquid crystal display device includes a first substrate constituting a base, a second substrate arranged to be opposite to the first substrate and to be an observation side, and a sealing material having a rectangular shape by which a gap is formed between the first substrate and the second substrate and then a liquid crystal layer is formed in the gap. In addition, first transparent driving electrodes are formed on the first substrate, second transparent driving electrodes extending in a direction substantially perpendicular to the first driving electrodes are formed on the second substrate, and the electrodes at the intersections of the first and second driving electrodes intersects and liquid crystal interposed therebetween constitute pixels. When a signal is supplied to each of the driving electrodes, a twist corresponding to the signal occurs in the liquid crystal disposed at each pixel. In this case, optical modulation is performed on light passing through the liquid crystal between the driving electrodes by the twist occurring in the liquid crystal.
Liquid crystal display devices include a transmissive liquid crystal display device which arranges a backlight device at the rear side of a first substrate and a reflective liquid crystal display device in which a light reflecting film is formed at a lower layer side of the first driving electrodes.
The transmissive liquid crystal display device displays a predetermined image by performing optical modulation on light emitted from the backlight device while it passes an electro-optical material layer. The reflective liquid crystal display device displays a predetermined image by reflecting external light incident from a second substrate side by a light reflecting film and performing optical modulation while the external light is emitted again from the second substrate.
Further, liquid crystal display devices include a transflective liquid crystal display device. The transflective liquid crystal display device arranges a backlight device at the rear side of the first substrate and forms a light reflecting film having light transmissive holes at a lower layer side of a first driving electrode. The transflective liquid crystal display device transmits light emitted from the backlight device through the light transmission holes to display an image (hereinafter, referred to as a transmissive mode). In addition, the transflective liquid crystal display device reflects incident external light by a light reflecting film in a region in which no light transmission hole is formed to display an image (hereinafter, referred to as a reflective mode).
In order to display an image on the liquid crystal display device, a driver IC for supplying a predetermined signal to both the first driving electrodes and the second electrodes needs to be provided. A method for installing the driver IC in the liquid crystal display device includes a method for installing the driver IC on both the first substrate and the second substrate, respectively and a method for installing the driver IC on one of the first and second substrates.
Therefore, in order to minimize the size of the liquid crystal display device and form a large image display region, a method for forming a protruding region protruding from the second substrate relative to the first substrate and installing the driver IC on the protruding region has been used.
A mounting terminal, on which the driver IC is directly mounted in the protruding region or a flexible substrate to which the driver IC is connected is mounted, is formed in the protruding region. In order to connect the first driving electrodes and the second driving electrodes to the mounting terminal, a first inter-substrate conducting terminal, a first wiring pattern, and a second wiring pattern, which will be described later, are formed on the first substrate, and a second inter-substrate conducting terminal, which will be described later, is formed on the second substrate.
Here, the first wiring pattern is a wiring line for electrically connecting the mounting terminal to the first driving electrodes. The first inter-substrate conducting terminal is formed in a region overlapping the second substrate, and the second wiring pattern is a wiring line for connecting the mounting terminal to the first inter-substrate conducting terminal. The second inter-substrate conducting terminal on the second substrate is formed in a position opposite to the first inter-substrate conducting terminal.
In addition, the first substrate and the second substrate are bonded to each other at a predetermined gap by a sealing material containing conductive particles. The conductive particles electrically connect the first inter-substrate conducting terminal and the second inter-substrate conducting terminal.
In this way, the mounting terminal and the first driving electrode are connected only by the first wiring pattern. In addition, the mounting terminal and the second driving electrode are connected by the second wiring pattern, the first inter-substrate conducting terminal, the conductive particles, and the second inter-substrate conducting terminal.
However, a material, such as a transparent conductive film (for example, an indium tin oxide (ITO) film) forming the first driving electrode, has been used to form the first wiring pattern and the second wiring pattern.
The ITO film used to form the first and second wiring patterns has greater electrical resistance than a metal material does. As a result, wiring resistance of the first wiring pattern and the second wiring pattern becomes remarkably great.
The present invention has been made to address the aforementioned problem, and it is an object of the present invention to provide an electro-optical device and an electronic apparatus in which it is possible to reduce wiring resistance.